-LRB- CNN -RRB- -- Sweden 's military feels certain there was an intruder , but it has called off the search for a mystery vessel in waters near Stockholm .

`` At least one '' foreign vessel was there , Swedish Rear Adm. Anders Grenstad said Friday . `` It may have been a small vessel . ''

Whatever may have been lurking beneath the waves of the archipelago for a week drew threats of martial force from Sweden 's military . A spokeswoman warned that the navy was `` prepared to use anything necessary '' to force the vessel to rise to the surface . The military used battleships , minesweepers and helicopters in the search .

Government officials have not said what they believed they had detected , but Sweden 's media reported the military was probably looking for a Russian submarine .

Report : Russian signal

Swedish intelligence had picked up a radio distress call last week -- in Russian -- which set off the defensive reconnaissance , major daily newspaper Svenska Dagbladet reported .

The transmissions were directed at the Russian enclave of Kaliningrad , 330 miles -LRB- 530 kilometers -RRB- south of Stockholm , on the Baltic 's southern shore , The Local reported .

Moscow said it had no vessel in Swedish waters and suggested Sweden ask the Netherlands if it was one of theirs stationed nearby .

The Netherlands is a member of a NATO and an ally of Sweden 's , which does not belong to the alliance . According to a report , the Dutch said they did not had a sub in Swedish waters .

Russia has recently flexed its muscles at Sweden , which has been cooperating recently more closely with NATO , security expert Gary Schmitt wrote in an analysis for CNN .

Moscow has practiced mock attacks of Stockholm and has flown very close to Swedish planes and ships , he said . It has also encroached upon Swedish airspace .

Tourist sub mix-up

The mystery had unpleasant side effects for tour guide Lasse Schmidt .

He putters around the archipelago with tourists in a small decommissioned military sub originally designed as a target for naval battle exercises .

And the national defense stir had some of his countrymen gunning for him .

They thought his submersible was what the navy detected as a potential intruder . The news of the military 's search had Schmidt 's business phone ringing , mostly with annoying calls .

`` Many people believe we caused this military operation , '' he said , `` and they call to demand that we pay the bill for it . ''

CNN 's Ralph Ellis , Lucy Pawle , Brad Lendon and Jason Hanna contributed to this report .

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Admiral : `` At least one '' foreign vessel was in Swedish waters

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Helicopters , battleships and minesweepers hunted for the vessel

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Emergency radio call in Russian was picked up by Swedish military , report says

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Russia denies that any vessel was in Swedish waters